Acceptance Test-Driven Development (ATDD)

Workflow

ATDD extends TDD by adding an outer acceptance test loop:

1. •Write an acceptance test that describes the desired behavior from the user's perspective
2. •Run it — it should fail (the feature doesn't exist yet)
3. •Enter the TDD inner loop:
   • •Write a failing unit test (RED)
   • •Write minimal code to pass (GREEN)
   • •Refactor (REFACTOR)
   • •Repeat until the acceptance test passes
4. •Verify the acceptance test passes — the feature is complete

Acceptance Test Patterns

Acceptance tests should be named with these patterns:

• •*.acceptance.test.ts — acceptance/integration tests
• •*.e2e.test.ts — end-to-end tests

Key Principles

• •Acceptance tests describe WHAT, not HOW — they test observable behavior
• •Unit tests describe HOW — they test internal mechanics
• •Write acceptance tests in the language of the user/stakeholder
• •One acceptance test per user story or feature
• •Multiple unit tests per acceptance test — the inner TDD loop

Example Workflow

Feature: User registration

1. Write acceptance test: user-registration.acceptance.test.ts
   - Test: "User can register with email and password"
   - Test: "Registration fails with duplicate email"
   - Run → FAIL (no registration endpoint)

2. TDD inner loop:
   a. Unit test: validate-email.test.ts → RED → implement → GREEN
   b. Unit test: hash-password.test.ts → RED → implement → GREEN
   c. Unit test: create-user.test.ts → RED → implement → GREEN
   d. Unit test: registration-handler.test.ts → RED → implement → GREEN

3. Run acceptance test → PASS → Feature complete!

Anti-Patterns to Avoid

• •❌ Writing unit tests without an acceptance test that frames the feature
• •❌ Writing acceptance tests that test implementation details
• •❌ Skipping the acceptance test because "it's a small feature"
• •❌ Writing all acceptance tests upfront (write them one feature at a time)